Abrasion-resistant pig, and materials and methods for making same

ABSTRACT

A pig for determining characteristics of a pipeline wall though which the pig passes has a sensor body that includes wear-resistant parts. The wear resistant parts contain polyurethane and have surfaces that are configured to contact the pipeline wall. At least one wear resistant part also includes a non-conductive hard filler.

BACKGROUND OF THE INVENTION

This present invention relates to pigs used in oil and gas pipelines todiagnose defects in pipeline walls, and more particularly, to pigs withextended lifetime, and the methods and materials useful for extendingthe lifetime of such pigs.

The use of pigs as in-line inspection tools is known as a method fordetecting cracks and corrosion. The pig can be placed in an oil or gaspipeline and propelled by pressure from the product being sent throughthe line. It is common practice to insert an intelligent pig into apipeline and move the pig through the pipeline as an in-line inspectiontool. The pig usually has urethane cups located in a front towingportion that seal with the pipeline wall and tow the intelligent portionof the pig through the pipeline by either gas or oil (fluids) in thepipeline pushing the cups as this product flows in the pipeline. Theintelligent portion of the pig collects data concerning defects in thepipeline wall as it is towed through the pipeline. The informationcollected on these anomalies comprises, for example, the location, sizeand shape of cracks, pits, dents and corrosion in the pipeline wall.This information is stored in the pig and later retrieved from the pigwhen it is removed from the pipeline. This information can then beanalyzed and the pipeline repaired as needed.

It is known for the intelligent pig in-line inspection tool to measurethe magnetic flux leakage associated with defects in pipeline walls. Thetool accomplishes this by magnetizing the pipeline wall and usingsensors to measure the leakage field generated by any defects. Themagnetic field is usually constant when no defects in the wall arepresent and as a result no leakage is detected. When there is a defectin the wall, the magnetic field induced by the pig in the pipeline wallbecomes more concentrated and increased leakage of magnetic fieldsdevelop which are measured to obtain information about the defect in thepipeline wall.

U.S. Pat. No. 6,847,207 issued Jan. 25, 2005 discloses an inspectiontool that measures magnetic flux leakage in the pipeline wall caused byanomalies in the pipeline wall. Magnetic flux leakage measuringtechnology relies on hall effect sensors to measure the magnitude of thedefect that causes the flux leakage to occur. The location of the defectin the pipe wall, that is closer to the inside diameter (ID) or outsidediameter (OD) cannot be determined from magnetic flux leakage measuringtechnology due to the physics of the magnetic flux leakage paths aroundthe defect. U.S. Pat. No. 6,847,207 teaches that ID/OD discrimination isaccomplished by using an eddy current pulser coil and an eddy currentdetection coil, or a two coil pair, to provide a signal used to indicatewhether a detected flux leakage anomaly is in the interior surface ofthe pipeline wall.

Although various known types of pigs perform their function well, theyare subject to wear as they pass through a pipeline and over defects ina pipeline. In particular, urethane cups and moldings around magneticflux sensors are subject to wear as the pigs ride along the inside of apipeline. This wear limits the useful life of these pigs.

BRIEF DESCRIPTION OF THE INVENTION

Therefore, one aspect of the present invention provides a pig fordetermining characteristics of a pipeline wall though which the pigpasses, the pig having a sensor body that includes wear-resistant parts.The wear resistant parts contain polyurethane and have surfaces that areconfigured to contact the pipeline wall. At least one wear resistantpart also includes a non-conductive hard filler.

Another aspect of the present invention provides a method for making asensor body cover for a pig. The method includes placing a circuit boardin a mold and putting a mixture of uncured polyurethane andnon-conductive particles into the mold and allowing it to cure.

Yet another aspect of the present invention provides a method for makinga sensor body cover for a pig. The method includes placing a circuitboard in a mold, putting a mixture of uncured polyurethane andnon-conductive particles into the mold to create a sledge covering partof the circuit board and allowing the sledge to cure, and puttinguncured polyurethane into the mold to create a bottom body part andallowing the bottom body part to cure.

It will be appreciated that the present invention provides longer lifeand wear resistance as compared to pigs that do not contain the wearresistant materials disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an intelligent pig foranalyzing anomalies in a pipeline wall according to an embodiment of thepresent invention.

FIG. 2 is a side view of the instrument portion of the pig shown in FIG.1.

FIG. 3 is a cross-sectional view of a configuration of sensor body.

FIG. 4 is a perspective side view of a configuration of an assembly of asensor head.

FIG. 5 is a bottom view of the sensor head configuration of FIG. 4.

FIG. 6 is another perspective view of the sensor head configuration ofFIG. 4 from another angle.

FIG. 7 is an electrical architectural overview of a configuration of asensor head.

DETAILED DESCRIPTION OF THE INVENTION

Some configurations of the present invention provide a pig having sensormolding(s) and/or cup molding(s) comprising a suitable plasticcomposition such as urethane combined with a hard filler. For use withmagnetic sensors, the hard filler should be non-conductive. Suitablenon-conductive hard fillers include, for example, silicon carbide. (Themolding is intended to be wear-resistant, but not necessarily abrasive.)The shape of the molding and the amount of filler material are selectedto extend the wear life out to greater than 400 km in someconfigurations, based on operational data using Caliper tools. In someconfigurations, a sensor is provided that comprises a non-conductivewear surface normally in contact with the inside wall of the pipelinethat permits for a suitable amount of energy transfer in both directionsbetween the single coil and the pipeline wall. The non-conductive wearresistant surface may comprise a polymer material, such as, for example,a polyurethane filled with wear resistant particles. The wear resistantparticles may comprise particles selected from the group consisting ofsilicon carbide and/or other non-conductive fillers, such as diamondchips.

More particularly, various parts of the pig that comprise polyurethaneand have surfaces that are intended to, or that may contact a pipe beinginspected, can comprise a polyurethane that has wear resistant particlesdistributed throughout.

In some configurations of the present invention there is provided asensor body for use in a pig for determining characteristics of apipeline wall though which the pig passes. The sensor body comprises acircuit board, a single coil wrapped around the circuit board, and amicrocontroller mounted to the circuit board. The microcontroller isconnected with the single coil for inducing a waveform in the coil tothereby create an eddy current in the pipeline wall adjacent the sensorbody. The microcontroller measures changes in a characteristic of theinduced waveform on the single coil that correspond to the presence ofanomalies on an inside diameter of the pipeline wall. The sensor bodyfurther comprises a sensor body cover molded about the circuit board,the microcontroller and the single coil. The sensor body cover consistsessentially of a wear resistant, non-conductive polymer material.

Referring now to FIG. 1, an intelligent pig 10 is shown for analyzinganomalies in pipeline walls. The pig 10 comprises a tow portion 12, aninstrument portion 14 and a data storage portion 16. Adjacent portions12, 14 and 14, 16 are connected by a universal joint 22 that permitsmovement of the pig 10 around bends in the pipeline. In the embodimentshown, the tow portion 12 houses the batteries for providing electricalpower to the pig. Annular cups 20 are mounted around the circumferenceof the tow portion for sealing the annulus between the tow portion 12and the pipeline wall 21. It should be understood that the tow portion12 may comprise multi-diameter cups that can expand and contract toconform with changes in the diameter of the pipeline. The flow ofpipeline fluid, such as, for example, natural gas or oil is trapped bythe cups causing the flowing fluid to push the pig through the pipeline.

The data storage portion 16 has a data memory for the pig 10. Dataconcerning the analysis of anomalies in the pipeline wall aretransmitted from sensors contained in the instrument portion 14 forstorage in memory. This data is analyzed after the pig is removed fromthe pipeline.

It should be understood that while the three portions of the pig areshown as separate sections interconnected by universal joints, inalternative embodiments, the pig 10 may comprise a single section thathouses the battery, instruments, and memory.

Referring to FIG. 1, circumferentially spaced suspension wheels 26 aremounted at the ends of each portion 12, 14, 16 for engagement with theinside of the pipeline wall and, together with the cups 20, to stabilizethe portions of the pig 10 relative to the pipeline wall.

Referring to FIG. 2, the instrument portion 14 of the pig 10 is shown tohave a central body 30, which is supported by a plurality ofcircumferentially spaced apart suspension wheels 26 mounted adjacentopposing ends of the central body 30. The wheels 26 support theinstrument portion 14 in the pipeline. Attached to the central body, forradial movement relative thereto, are a plurality circumferentiallyspaced apart arms 34. The radial movement of the arms 34 relative to thecentral body 30 provides clearance for the instrument portion 14 pig 10in the event that it encounters obstructions as it travels through thepipeline.

Magnets 42, 42 a of opposite polarity are mounted on the arms 34 onopposing sides of a sensor body 50 for generating and transmitting amagnetic field through portions of the pipeline wall 21 adjacent thesensor body 50.

A sensor body 50 is mounted to each arm 34. As shown in FIG. 3, sensorbody 50 comprises a circuit board 52, a single coil 54 wrapped aroundthe circuit board 52, a plurality of magnetic flux leakage measuringdevices 56 mounted on the circuit board 52, and a microcontroller 58mounted to the circuit board 52. The microcontroller 58 is connectedwith the magnetic flux leakage measuring devices 56 for detecting fluxleakage in the pipeline wall 21. The magnetic flux leakage devices 56each comprise a hall effect sensing device. The microprocessor 58 isalso connected with the single coil 54 for inducing a waveform on thecoil 54 to thereby create an eddy current in the pipeline wall 21adjacent the sensor body 50. The microcontroller 58 measures changes inthe peak-to-peak amplitude of the induced waveform on the single coil 54that correspond to the presence of anomalies on an inside of thepipeline wall. In some configurations, sensor body 50 further comprisesa sensor body cover 60 comprising a sledge 64 and a bottom cover 66,both molded about circuit board 52, the microcontroller 58, the halleffect sensing devices 56 and the single coil 54. Sledge 64 consistsessentially of a wear resistant, non-conductive polymer material, suchas for example, polyurethane filled with a wear resistant filler such assilicon carbide and/or other non-conductive fillers. (“Non-conductive,”as used herein, means “electrically non-conductive,” unless otherwiseexplicitly stated. Another suitable non-conductive filler may includediamond chips.) Bottom cover 66 consists essentially of a polyurethanewithout the silicon carbide or other non-conductive fillers. Forexample, in some configurations, board 52, including hall effect sensingdevices 56 and single coil 54 are placed in a mold and a mixture ofuncured polyurethane and silicon carbide poured in up to the intendeddepth of sledge 64. This sledge is allowed to cure, and a polyurethaneepoxy compound is poured on top of sledge 64 and allowed to cure to formbottom cover 66. Thus, sledge 64, in effect, forms a sort of “laminate”over the face of sensor cover 60 that provides hardness and extendedwear resistance as pig 10 moves against pipe wall 21. (Indexing pins,not shown, can be used to hold circuit board 52 in place in the mold.)

In some configurations of the present invention, sensor body cover 60 ishomogeneous and, in its entirety, consists essentially of eitherpolyurethane without silicon carbide or other fillers, or polyurethanewith silicon carbide and/or other non-conductive fillers. In this case,there is no need to create a separate sledge. Instead, the mold isfilled to the intended depth to create the entire sensor body cover 60and allowed to cure with circuit board 52 embedded therein.

The use of silicon carbide or other hard, non-conductive fillerssubstantially increases the life of sensor bodies 50. In someconfigurations, #36 grit silicon carbide (SiC) particles pretreated withsilane is used. (Silane washing can be performed by vendors of siliconcarbide. Untreated SiC particles can also be used.) A suitablepolyurethane resin used in some configurations is RenCast™ 6444/Ren®6444polyurethane (available from RenShape Solutions, East Lansing, Mich.),which is a semi-rigid, amber, two component polyurea elastomer suitablefor wear resistant applications. At an early stage of mixing thepolyurethane resin, the SiC particles are added and mixed in thoroughly.In some configurations, the mixture is centrifuged and/or placed in avacuum before use to remove air that may be trapped by the mixing. Anyamount of #36 grit SiC in this material up to at least about 20% byweight increases the wear resistance and lifetime of sensor bodies 50,and particularly sledge 64, although in experiments, 10% by weight SiChas been found to outlast sledges 64 of 20% by weight SiC. For example,at least about 1% by weight SiC can be used, or at least about 5% byweight SiC can be used, or at least about 10% by weight SiC can be used,or at least about 15% by weight SiC can be used, up to about 20% byweight SiC. The use of over 20% by weight SiC may be possible in someconfigurations.

In particular, tests on actual sensor bodies 50 using 10% by weight SiCin sledge 64 consistently showed less than 2.0 mm of abrasive wear aftermore than 236 km of run on a test track. In some test runs, about 1800km of run on a test track produced 1.41 mm of wear or less. Sensorbodies having sledges of 20% by weight SiC produced 1.04 mm of wear orless after 686 km of run on a test track, as compared to 0.93 and 0.73mm for two different sensor bodies having 10% by weight sledges. Sensorbodies without SiC were found to have wear of 1.4 and 1.2 mm after only14 km.

In some configurations of the present invention, SiC (or othernon-conductive filler) is also used for annular cups 20. For example,annular cups 20 in some configurations consist essentially of the samecomposition used for sledges 64. This composition advantageously reduceswear on annular cups 20.

FIG. 4 is a side perspective view of a configuration of an assembly of asensor head 80 that comprises four sensor bodies 50. Each sensor body 50is supported by a spring support 82 that comprises or consistsessentially of a material softer or less dense than polyurethane orother suitable non-conductive material. Spring support 82 can be moldedusing suitable polyurethane epoxy, for example, so that entire sensorhead assembly 80 is a unitary component. An electrical cable 87(partially shown in FIG. 5) from each sensor body 50 that communicateswith microcontroller 58 and provides power and ground is embedded withina respective arm 84. These cables connect to a marshalling card 86,shown in the bottom view of FIG. 5. Marshalling card 86 is actuallyembedded in bottom section 88 of spring support 82, but is shown in FIG.5 because in some configurations, bottom section 88 is transparent orsemitransparent. Marshalling card 86 concatenates and packetizes datafrom all four sensor bodies 50 and provides this data for furtherprocessing through a power and data cable 90 that exits sensor head 80.A perspective view of sensor head assembly 80 is shown in FIG. 6. Inconfigurations of the present invention in which silicon carbide orother non-conductive material is used in a sledge 64 or in sensor cover60 in its entirety, imperfections in a pipe wall that contact slopedsurface 92 may cause spring support 82 to bend slightly to conform, butthe portion of surface 92 that contacts this imperfection would beprotected by the harder material out of which sledge 64 (or sensor cover60) is made.

The single coil 54 together with the microcontroller 58 provide ID/ODdiscrimination used to assist in the determination of the location ofthe defect relative to the inside diameter or outside diameter of thepipeline 21. The microcontroller 58 measures the change in peak-to-peakamplitude of an induced waveform on a single coil 54. The peak-to-peakamplitude varies with its proximity to metallic objects; therefore ifthere is corrosion on the inside of the pipe, the microcontroller 58senses the absence of metal, and if the corrosion is on the outside ofthe pipe there will be no measurable change in the single coil. Usingthe single coil 54 can in combination with the hall effect sensingdevice information, the microcontroller discern both magnitude andlocation of a defect.

In some configurations and referring to FIG. 7, an architecturaloverview of a configuration of sensor head 62 used in someconfigurations of the present invention includes a plurality of Halleffect sensing devices 56 including two axial sensors and two radialsensors, a single eddy current coil 54, microcontroller ormicroprocessor 58, eddy current driver 70, a power supply 72, and anelectrostatic discharge (ESD) clamp 74. Voltage, data, clock, and groundsignals are provided via a cable. Microcontroller 58 manages digital toanalog conversion functions, data telemetry, data processing, and eddycoil driver functions. Data and commands in some configurations arecommunicated between a host and sensor head 62 is over a half-duplexbidirectional synchronous data link supported directly bymicrocontroller 58 at a data rate of 1 megabit per second. Also in someconfigurations, electronics in sensor head 62 is a slave to the host. Asa result, the host is responsible for managing the timing of command anddata transfer operations. Data and clock signal lines are protectedagainst ESD events by ESD clamp 74. Hall sensors 56 are, in someconfigurations, low noise linear Hall effect devices selected forappropriate flux sensitivity, turn-on time, and noise specifications,and are radiometric to the power supply. In operation, Hall sensors 56are normally turned off in some configurations, except during a samplecycle. At the start of a sample cycle, Hall sensors 56 are turned on,allowed to stabilize, sampled by an analog to digital converter inmicrocontroller 58, and then turned off. This sequence of eventsadvantageously reduces the current consumption of sensor head 62.

Eddy coil 54 is used to measure a distance between sensor head surface76 and pipeline wall 25 and in determining a fault location (ID or OD).In this use, microcontroller 58 excites eddy coil 54. A peak-to-peakmeasurement is made of a resulting waveform and the liftoff is derivedfrom data contained in a calibration table stored in microcontroller 58.

The microcontroller single coil ID/OD sensing works as follows. A smallcoil 52 whose physical location is very close to the pipe wall (between0 and 10 mm) is driven with a square wave signal from themicrocontroller 58. The driving frequency of coil 52 is the free airresonant frequency of a tank circuit comprising coil 52 and a capacitor(not shown) on the same board as microcontroller 58. Coil 52 convertsthe electrical energy from the driving signal into a magnetic fieldwhich, when in range of the metallic object in question, induces an eddycurrent within the metallic object, resulting in a transfer of theenergy into the metallic object. The driving frequency (and thus thecapacitance of the on-board capacitor) is chosen to be high enough sothat the metal is lossy at the driving frequency, yet low enough so thatit can be adequately sampled by an analog to digital converter inmicrocontroller 58. Some configurations of the present invention utilizedriving frequencies of 28 kHz to 40 kHz, for example, but higher andlower frequencies can be used as a design choice.

During the driving sequence of 4 to 5 square waveform pulses, forexample, the amplitude of the drive signal is measured on a capacitivelyisolated side of the coil by the microcontroller 58. The amplitude ofthe high and low peaks are quantified by the analog to digital converterand subtracted. The net result is a peak to peak amplitude associatedwith the induced waveform in the coil 52, which amplitude isproportional to the coil's proximity to the target metallic object.Therefore, if the sensor body 50 is riding along a pipewall 21 and itsdistance increases (due to a pitting in the metal surface), a change inmeasured peak-to-peak amplitude signals that the sensor body 50 haslifted off from the metal surface. The liftoff is measured by means ofmeasuring both the peak and trough of the induced waveform in responseto the proximity of the coil to the metallic surface. Because themicrocontroller 54 measures change in peak to peak amplitude, thismeasurement is immune to the effects of velocity (greater losses due tomoving the sensor across a metallic surface—eddy current losses increaseas a result).

Because the driving frequency of coil 52 is the resonant circuit of thetank circuit in free air, the effect of coil 52 passing over a defect isin the real domain rather than the imaginary. The amplitude is shiftedmeasurably as a result. As a result, the effect of passing through astray magnetic field can be cancelled out so that only the standoff fromthe pipe and/or the presence or absence of a defect is detected orrecognized in some configurations of the present invention.

In some configurations of the present invention, one or more functionsof sensor head 62 are overlapped to reduce overall cycle time. Also,some configurations ensure that data transmission is not active duringacquisition of data from sensors 56 so that spurious electrical noise isreduced during the analog to digital conversion process.

It will thus be appreciated that the present invention provides longerlife and wear resistance as compared to pigs that do not contain thewear resistant materials disclosed herein.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A pig for determining characteristics of a pipeline wall though whichthe pig passes, the pig having a sensor body that includeswear-resistant parts comprising polyurethane and having surfaces thatare configured to contact the pipeline wall, wherein at least one saidwear-resistant part includes a non-conductive hard filler.
 2. A pig inaccordance with claim 1 wherein said wear-resistant parts include asensor body cover that includes the non-conductive hard filler.
 3. A pigin accordance with claim 2 wherein said wear-resistant parts include asledge that includes the non-conductive hard filler, wherein said sledgeis part of a sensor body cover.
 4. A pig in accordance with claim 3wherein said non-conductive hard filler comprises silicon carbide.
 5. Apig in accordance with claim 2 wherein said sensor body cover comprisessilicon carbide.
 6. A pig in accordance with claim 1 wherein saidwear-resistant parts include an annular cup.
 7. A pig in accordance withclaim 1 wherein said parts including a non-conductive hard fillerconsist essentially of polyurethane, with between 1% and 20% by weightSiC.
 8. A pig in accordance with claim 1 wherein said parts including anon-conductive hard filler consist essentially of polyurethane, withbetween 5% and 15% by weight SiC.
 9. A pig in accordance with claim 8,wherein said SiC is #36 grit.
 10. A pig in accordance with claim 9,wherein said wear-resistant parts including the non-conductive hardfiller include an annular cup and at least sledges of sensor bodycovers.
 11. A method for making a sensor body cover for a pig, saidmethod comprising: placing a circuit board in a mold; and putting amixture of uncured polyurethane and non-conductive particles into themold and allowing the mixture to cure.
 12. A method in accordance withclaim 11 wherein said non-conductive particles comprise SiC.
 13. Amethod in accordance with claim 12 wherein said SiC particles are #36grit.
 14. A method in accordance with claim 12 wherein said SiCparticles comprise between 1% and 20% by weight of the mixture ofpolyurethane and non-conductive particles.
 15. A method in accordancewith claim 14 wherein said SiC particles comprise between 5% and 15% byweight of the mixture of polyurethane and non-conductive particles. 16.A method for making a sensor body cover for a pig, said methodcomprising: placing a circuit board in a mold; putting a mixture ofuncured polyurethane and non-conductive particles into the mold tocreate a sledge covering part of the circuit board and allowing thesledge to cure; and putting uncured polyurethane into the mold to createa bottom body part and allowing the bottom body part to cure.
 17. Amethod in accordance with claim 16 wherein said non-conductive particlescomprise SiC.
 18. A method in accordance with claim 17 wherein said SiCparticles are #36 grit.
 19. A method in accordance with claim 17 whereinsaid SiC particles comprise between 1% and 20% by weight of the mixtureof polyurethane and non-conductive particles.
 20. A method in accordancewith claim 19 wherein said SiC particles comprise between 5% and 15% byweight of the mixture of polyurethane and non-conductive particles.